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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Sliced VBI Data Interface</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="LINUX MEDIA INFRASTRUCTURE API" /><link rel="up" href="ch04.html" title="Chapter 4. Interfaces" /><link rel="prev" href="ch04s07.html" title="Raw VBI Data Interface" /><link rel="next" href="ch04s09.html" title="Teletext Interface" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Sliced VBI Data Interface</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch04s07.html">Prev</a> </td><th width="60%" align="center">Chapter 4. Interfaces</th><td width="20%" align="right"> <a accesskey="n" href="ch04s09.html">Next</a></td></tr></table><hr /></div><div class="section" title="Sliced VBI Data Interface"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="sliced"></a>Sliced VBI Data Interface</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="ch04s08.html#id2658885">Querying Capabilities</a></span></dt><dt><span class="section"><a href="ch04s08.html#id2658932">Supplemental Functions</a></span></dt><dt><span class="section"><a href="ch04s08.html#sliced-vbi-format-negotitation">Sliced VBI Format Negotiation</a></span></dt><dt><span class="section"><a href="ch04s08.html#id2659926">Reading and writing sliced VBI data</a></span></dt><dt><span class="section"><a href="ch04s08.html#id2660280">Sliced VBI Data in MPEG Streams</a></span></dt></dl></div><p>VBI stands for Vertical Blanking Interval, a gap in the
sequence of lines of an analog video signal. During VBI no picture
information is transmitted, allowing some time while the electron beam
of a cathode ray tube TV returns to the top of the screen.</p><p>Sliced VBI devices use hardware to demodulate data transmitted
in the VBI. V4L2 drivers shall <span class="emphasis"><em>not</em></span> do this by
software, see also the <a class="link" href="ch04s07.html" title="Raw VBI Data Interface">raw VBI
interface</a>. The data is passed as short packets of fixed size,
covering one scan line each. The number of packets per video frame is
variable.</p><p>Sliced VBI capture and output devices are accessed through the
same character special files as raw VBI devices. When a driver
supports both interfaces, the default function of a
<code class="filename">/dev/vbi</code> device is <span class="emphasis"><em>raw</em></span> VBI
capturing or output, and the sliced VBI function is only available
after calling the <a class="link" href="re41.html" title="ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT"><code class="constant">VIDIOC_S_FMT</code></a> ioctl as defined below. Likewise a
<code class="filename">/dev/video</code> device may support the sliced VBI API,
however the default function here is video capturing or output.
Different file descriptors must be used to pass raw and sliced VBI
data simultaneously, if this is supported by the driver.</p><div class="section" title="Querying Capabilities"><div class="titlepage"><div><div><h3 class="title"><a id="id2658885"></a>Querying Capabilities</h3></div></div></div><p>Devices supporting the sliced VBI capturing or output API
set the <code class="constant">V4L2_CAP_SLICED_VBI_CAPTURE</code> or
<code class="constant">V4L2_CAP_SLICED_VBI_OUTPUT</code> flag respectively, in
the <em class="structfield"><code>capabilities</code></em> field of struct <a class="link" href="re56.html#v4l2-capability" title="Table A.66. struct v4l2_capability">v4l2_capability</a>
returned by the <a class="link" href="re56.html" title="ioctl VIDIOC_QUERYCAP"><code class="constant">VIDIOC_QUERYCAP</code></a> ioctl. At least one of the
read/write, streaming or asynchronous <a class="link" href="ch03.html" title="Chapter 3. Input/Output">I/O
methods</a> must be supported. Sliced VBI devices may have a tuner
or modulator.</p></div><div class="section" title="Supplemental Functions"><div class="titlepage"><div><div><h3 class="title"><a id="id2658932"></a>Supplemental Functions</h3></div></div></div><p>Sliced VBI devices shall support <a class="link" href="ch01s04.html" title="Video Inputs and Outputs">video
input or output</a> and <a class="link" href="ch01s06.html" title="Tuners and Modulators">tuner or
modulator</a> ioctls if they have these capabilities, and they may
support <a class="link" href="ch01s08.html" title="User Controls">control</a> ioctls. The <a class="link" href="ch01s07.html" title="Video Standards">video standard</a> ioctls provide information
vital to program a sliced VBI device, therefore must be
supported.</p></div><div class="section" title="Sliced VBI Format Negotiation"><div class="titlepage"><div><div><h3 class="title"><a id="sliced-vbi-format-negotitation"></a>Sliced VBI Format Negotiation</h3></div></div></div><p>To find out which data services are supported by the
hardware applications can call the <a class="link" href="re49.html" title="ioctl VIDIOC_G_SLICED_VBI_CAP"><code class="constant">VIDIOC_G_SLICED_VBI_CAP</code></a> ioctl.
All drivers implementing the sliced VBI interface must support this
ioctl. The results may differ from those of the <a class="link" href="re41.html" title="ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT"><code class="constant">VIDIOC_S_FMT</code></a> ioctl
when the number of VBI lines the hardware can capture or output per
frame, or the number of services it can identify on a given line are
limited. For example on PAL line 16 the hardware may be able to look
for a VPS or Teletext signal, but not both at the same time.</p><p>To determine the currently selected services applications
set the <em class="structfield"><code>type </code></em> field of struct <a class="link" href="re41.html#v4l2-format" title="Table A.46. struct v4l2_format">v4l2_format</a> to
<code class="constant"> V4L2_BUF_TYPE_SLICED_VBI_CAPTURE</code> or <code class="constant">
V4L2_BUF_TYPE_SLICED_VBI_OUTPUT</code>, and the <a class="link" href="re41.html" title="ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT"><code class="constant">VIDIOC_G_FMT</code></a>
ioctl fills the <em class="structfield"><code>fmt.sliced</code></em> member, a
struct <a class="link" href="ch04s08.html#v4l2-sliced-vbi-format" title="Table 4.6. struct v4l2_sliced_vbi_format">v4l2_sliced_vbi_format</a>.</p><p>Applications can request different parameters by
initializing or modifying the <em class="structfield"><code>fmt.sliced</code></em>
member and calling the <a class="link" href="re41.html" title="ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT"><code class="constant">VIDIOC_S_FMT</code></a> ioctl with a pointer to the
<span class="structname">v4l2_format</span> structure.</p><p>The sliced VBI API is more complicated than the raw VBI API
because the hardware must be told which VBI service to expect on each
scan line. Not all services may be supported by the hardware on all
lines (this is especially true for VBI output where Teletext is often
unsupported and other services can only be inserted in one specific
line). In many cases, however, it is sufficient to just set the
<em class="structfield"><code>service_set</code></em> field to the required services
and let the driver fill the <em class="structfield"><code>service_lines</code></em>
array according to hardware capabilities. Only if more precise control
is needed should the programmer set the
<em class="structfield"><code>service_lines</code></em> array explicitly.</p><p>The <a class="link" href="re41.html" title="ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT"><code class="constant">VIDIOC_S_FMT</code></a> ioctl modifies the parameters
according to hardware capabilities. When the driver allocates
resources at this point, it may return an <span class="errorcode">EBUSY</span> error code if the required
resources are temporarily unavailable. Other resource allocation
points which may return <span class="errorcode">EBUSY</span> can be the
<a class="link" href="re61.html" title="ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF"><code class="constant">VIDIOC_STREAMON</code></a> ioctl and the first <a class="link" href="re66.html" title="V4L2 read()"><code class="function">read()</code></a>, <a class="link" href="re68.html" title="V4L2 write()"><code class="function">write()</code></a> and
<a class="link" href="re67.html" title="V4L2 select()"><code class="function">select()</code></a> call.</p><div class="table"><a id="v4l2-sliced-vbi-format"></a><p class="title"><b>Table 4.6. struct
<span class="structname">v4l2_sliced_vbi_format</span></b></p><div class="table-contents"><table summary="struct v4l2_sliced_vbi_format" width="100%" border="0"><colgroup><col /><col /><col /><col /><col /></colgroup><tbody valign="top"><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>service_set</code></em></td><td colspan="3" valign="top"><p>If
<em class="structfield"><code>service_set</code></em> is non-zero when passed with
<a class="link" href="re41.html" title="ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT"><code class="constant">VIDIOC_S_FMT</code></a> or <a class="link" href="re41.html" title="ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT"><code class="constant">VIDIOC_TRY_FMT</code></a>, the
<em class="structfield"><code>service_lines</code></em> array will be filled by the
driver according to the services specified in this field. For example,
if <em class="structfield"><code>service_set</code></em> is initialized with
<code class="constant">V4L2_SLICED_TELETEXT_B | V4L2_SLICED_WSS_625</code>, a
driver for the cx25840 video decoder sets lines 7-22 of both
fields<sup>[<a id="id2659285" href="#ftn.id2659285" class="footnote">a</a>]</sup> to <code class="constant">V4L2_SLICED_TELETEXT_B</code>
and line 23 of the first field to
<code class="constant">V4L2_SLICED_WSS_625</code>. If
<em class="structfield"><code>service_set</code></em> is set to zero, then the values
of <em class="structfield"><code>service_lines</code></em> will be used instead.
</p><p>On return the driver sets this field to the union of all
elements of the returned <em class="structfield"><code>service_lines</code></em>
array. It may contain less services than requested, perhaps just one,
if the hardware cannot handle more services simultaneously. It may be
empty (zero) if none of the requested services are supported by the
hardware.</p></td></tr><tr><td valign="top">__u16</td><td valign="top"><em class="structfield"><code>service_lines</code></em>[2][24]</td><td colspan="3" valign="top"><p>Applications initialize this
array with sets of data services the driver shall look for or insert
on the respective scan line. Subject to hardware capabilities drivers
return the requested set, a subset, which may be just a single
service, or an empty set. When the hardware cannot handle multiple
services on the same line the driver shall choose one. No assumptions
can be made on which service the driver chooses.</p><p>Data
services are defined in <a class="xref" href="ch04s08.html#vbi-services2" title="Table 4.7. Sliced VBI services">Table 4.7, “Sliced VBI services”</a>. Array indices
map to ITU-R line numbers (see also <a class="xref" href="ch04s07.html#vbi-525" title="Figure 4.2. ITU-R 525 line numbering (M/NTSC and M/PAL)">Figure 4.2, “ITU-R 525 line numbering (M/NTSC and M/PAL)”</a> and <a class="xref" href="ch04s07.html#vbi-625" title="Figure 4.3. ITU-R 625 line numbering">Figure 4.3, “ITU-R 625 line numbering”</a>) as follows: </p></td></tr><tr><td valign="top"> </td><td valign="top"> </td><td valign="top">Element</td><td valign="top">525 line systems</td><td valign="top">625 line systems</td></tr><tr><td valign="top"> </td><td valign="top"> </td><td valign="top"><em class="structfield"><code>service_lines</code></em>[0][1]</td><td align="center" valign="top">1</td><td align="center" valign="top">1</td></tr><tr><td valign="top"> </td><td valign="top"> </td><td valign="top"><em class="structfield"><code>service_lines</code></em>[0][23]</td><td align="center" valign="top">23</td><td align="center" valign="top">23</td></tr><tr><td valign="top"> </td><td valign="top"> </td><td valign="top"><em class="structfield"><code>service_lines</code></em>[1][1]</td><td align="center" valign="top">264</td><td align="center" valign="top">314</td></tr><tr><td valign="top"> </td><td valign="top"> </td><td valign="top"><em class="structfield"><code>service_lines</code></em>[1][23]</td><td align="center" valign="top">286</td><td align="center" valign="top">336</td></tr><tr><td valign="top"> </td><td valign="top"> </td><td colspan="3" valign="top">Drivers must set
<em class="structfield"><code>service_lines</code></em>[0][0] and
<em class="structfield"><code>service_lines</code></em>[1][0] to zero.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>io_size</code></em></td><td colspan="3" valign="top">Maximum number of bytes passed by
one <a class="link" href="re66.html" title="V4L2 read()"><code class="function">read()</code></a> or <a class="link" href="re68.html" title="V4L2 write()"><code class="function">write()</code></a> call, and the buffer size in bytes for
the <a class="link" href="re54.html" title="ioctl VIDIOC_QBUF, VIDIOC_DQBUF"><code class="constant">VIDIOC_QBUF</code></a> and <a class="link" href="re54.html" title="ioctl VIDIOC_QBUF, VIDIOC_DQBUF"><code class="constant">VIDIOC_DQBUF</code></a> ioctl. Drivers set this field to
the size of struct <a class="link" href="ch04s08.html#v4l2-sliced-vbi-data" title="Table 4.8. struct v4l2_sliced_vbi_data">v4l2_sliced_vbi_data</a> times the number of non-zero
elements in the returned <em class="structfield"><code>service_lines</code></em>
array (that is the number of lines potentially carrying data).</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>reserved</code></em>[2]</td><td colspan="3" valign="top">This array is reserved for future
extensions. Applications and drivers must set it to zero.</td></tr></tbody><tbody class="footnotes"><tr><td colspan="5"><div class="footnote"><p><sup>[<a id="ftn.id2659285" href="#id2659285" class="para">a</a>] </sup>According to <a class="link" href="bi01.html#ets300706" title="ETS 300 706 "Enhanced Teletext specification"">ETS 300 706</a> lines 6-22 of the
first field and lines 5-22 of the second field may carry Teletext
data.</p></div></td></tr></tbody></table></div></div><br class="table-break" /><div class="table"><a id="vbi-services2"></a><p class="title"><b>Table 4.7. Sliced VBI services</b></p><div class="table-contents"><table summary="Sliced VBI services" width="100%" border="0"><colgroup><col /><col /><col /><col /><col /></colgroup><thead><tr><th>Symbol</th><th>Value</th><th>Reference</th><th>Lines, usually</th><th>Payload</th></tr></thead><tbody valign="top"><tr><td valign="top"><code class="constant">V4L2_SLICED_TELETEXT_B</code>
(Teletext System B)</td><td valign="top">0x0001</td><td valign="top"><a class="xref" href="bi01.html#ets300706" title="ETS 300 706 "Enhanced Teletext specification"">[<abbr class="abbrev">ETS 300 706</abbr>]</a>, <a class="xref" href="bi01.html#itu653" title="ITU-R Recommendation BT.653-3 "Teletext systems"">[<abbr class="abbrev">ITU BT.653</abbr>]</a></td><td valign="top">PAL/SECAM line 7-22, 320-335 (second field 7-22)</td><td valign="top">Last 42 of the 45 byte Teletext packet, that is
without clock run-in and framing code, lsb first transmitted.</td></tr><tr><td valign="top"><code class="constant">V4L2_SLICED_VPS</code></td><td valign="top">0x0400</td><td valign="top"><a class="xref" href="bi01.html#ets300231" title="ETS 300 231 "Specification of the domestic video Programme Delivery Control system (PDC)"">[<abbr class="abbrev">ETS 300 231</abbr>]</a></td><td valign="top">PAL line 16</td><td valign="top">Byte number 3 to 15 according to Figure 9 of
ETS 300 231, lsb first transmitted.</td></tr><tr><td valign="top"><code class="constant">V4L2_SLICED_CAPTION_525</code></td><td valign="top">0x1000</td><td valign="top"><a class="xref" href="bi01.html#eia608" title="EIA 608-B "Recommended Practice for Line 21 Data Service"">[<abbr class="abbrev">EIA 608-B</abbr>]</a></td><td valign="top">NTSC line 21, 284 (second field 21)</td><td valign="top">Two bytes in transmission order, including parity
bit, lsb first transmitted.</td></tr><tr><td valign="top"><code class="constant">V4L2_SLICED_WSS_625</code></td><td valign="top">0x4000</td><td valign="top"><a class="xref" href="bi01.html#itu1119" title="ITU-R Recommendation BT.1119 "625-line television Wide Screen Signalling (WSS)"">[<abbr class="abbrev">ITU BT.1119</abbr>]</a>, <a class="xref" href="bi01.html#en300294" title="EN 300 294 "625-line television Wide Screen Signalling (WSS)"">[<abbr class="abbrev">EN 300 294</abbr>]</a></td><td valign="top">PAL/SECAM line 23</td><td valign="top"><pre class="screen">
Byte 0 1
msb lsb msb lsb
Bit 7 6 5 4 3 2 1 0 x x 13 12 11 10 9
</pre></td></tr><tr><td valign="top"><code class="constant">V4L2_SLICED_VBI_525</code></td><td valign="top">0x1000</td><td colspan="3" valign="top">Set of services applicable to 525
line systems.</td></tr><tr><td valign="top"><code class="constant">V4L2_SLICED_VBI_625</code></td><td valign="top">0x4401</td><td colspan="3" valign="top">Set of services applicable to 625
line systems.</td></tr></tbody></table></div></div><br class="table-break" /><p>Drivers may return an <span class="errorcode">EINVAL</span> error code when applications attempt to
read or write data without prior format negotiation, after switching
the video standard (which may invalidate the negotiated VBI
parameters) and after switching the video input (which may change the
video standard as a side effect). The <a class="link" href="re41.html" title="ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT"><code class="constant">VIDIOC_S_FMT</code></a> ioctl may return
an <span class="errorcode">EBUSY</span> error code when applications attempt to change the format while i/o is
in progress (between a <a class="link" href="re61.html" title="ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF"><code class="constant">VIDIOC_STREAMON</code></a> and <a class="link" href="re61.html" title="ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF"><code class="constant">VIDIOC_STREAMOFF</code></a> call,
and after the first <a class="link" href="re66.html" title="V4L2 read()"><code class="function">read()</code></a> or <a class="link" href="re68.html" title="V4L2 write()"><code class="function">write()</code></a> call).</p></div><div class="section" title="Reading and writing sliced VBI data"><div class="titlepage"><div><div><h3 class="title"><a id="id2659926"></a>Reading and writing sliced VBI data</h3></div></div></div><p>A single <a class="link" href="re66.html" title="V4L2 read()"><code class="function">read()</code></a> or <a class="link" href="re68.html" title="V4L2 write()"><code class="function">write()</code></a> call must pass all data
belonging to one video frame. That is an array of
<span class="structname">v4l2_sliced_vbi_data</span> structures with one or
more elements and a total size not exceeding
<em class="structfield"><code>io_size</code></em> bytes. Likewise in streaming I/O
mode one buffer of <em class="structfield"><code>io_size</code></em> bytes must
contain data of one video frame. The <em class="structfield"><code>id</code></em> of
unused <span class="structname">v4l2_sliced_vbi_data</span> elements must be
zero.</p><div class="table"><a id="v4l2-sliced-vbi-data"></a><p class="title"><b>Table 4.8. struct
<span class="structname">v4l2_sliced_vbi_data</span></b></p><div class="table-contents"><table summary="struct v4l2_sliced_vbi_data" width="100%" border="0"><colgroup><col /><col /><col /></colgroup><tbody valign="top"><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>id</code></em></td><td valign="top">A flag from <a class="xref" href="re49.html#vbi-services" title="Table A.59. Sliced VBI services">Table A.59, “Sliced VBI services”</a>
identifying the type of data in this packet. Only a single bit must be
set. When the <em class="structfield"><code>id</code></em> of a captured packet is
zero, the packet is empty and the contents of other fields are
undefined. Applications shall ignore empty packets. When the
<em class="structfield"><code>id</code></em> of a packet for output is zero the
contents of the <em class="structfield"><code>data</code></em> field are undefined
and the driver must no longer insert data on the requested
<em class="structfield"><code>field</code></em> and
<em class="structfield"><code>line</code></em>.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>field</code></em></td><td valign="top">The video field number this data has been captured
from, or shall be inserted at. <code class="constant">0</code> for the first
field, <code class="constant">1</code> for the second field.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>line</code></em></td><td valign="top">The field (as opposed to frame) line number this
data has been captured from, or shall be inserted at. See <a class="xref" href="ch04s07.html#vbi-525" title="Figure 4.2. ITU-R 525 line numbering (M/NTSC and M/PAL)">Figure 4.2, “ITU-R 525 line numbering (M/NTSC and M/PAL)”</a> and <a class="xref" href="ch04s07.html#vbi-625" title="Figure 4.3. ITU-R 625 line numbering">Figure 4.3, “ITU-R 625 line numbering”</a> for valid
values. Sliced VBI capture devices can set the line number of all
packets to <code class="constant">0</code> if the hardware cannot reliably
identify scan lines. The field number must always be valid.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>reserved</code></em></td><td valign="top">This field is reserved for future extensions.
Applications and drivers must set it to zero.</td></tr><tr><td valign="top">__u8</td><td valign="top"><em class="structfield"><code>data</code></em>[48]</td><td valign="top">The packet payload. See <a class="xref" href="re49.html#vbi-services" title="Table A.59. Sliced VBI services">Table A.59, “Sliced VBI services”</a> for the contents and number of
bytes passed for each data type. The contents of padding bytes at the
end of this array are undefined, drivers and applications shall ignore
them.</td></tr></tbody></table></div></div><br class="table-break" /><p>Packets are always passed in ascending line number order,
without duplicate line numbers. The <a class="link" href="re68.html" title="V4L2 write()"><code class="function">write()</code></a> function and the
<a class="link" href="re54.html" title="ioctl VIDIOC_QBUF, VIDIOC_DQBUF"><code class="constant">VIDIOC_QBUF</code></a> ioctl must return an <span class="errorcode">EINVAL</span> error code when applications violate
this rule. They must also return an <span class="errorcode">EINVAL</span> error code when applications pass an
incorrect field or line number, or a combination of
<em class="structfield"><code>field</code></em>, <em class="structfield"><code>line</code></em> and
<em class="structfield"><code>id</code></em> which has not been negotiated with the
<a class="link" href="re41.html" title="ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT"><code class="constant">VIDIOC_G_FMT</code></a> or <a class="link" href="re41.html" title="ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT"><code class="constant">VIDIOC_S_FMT</code></a> ioctl. When the line numbers are
unknown the driver must pass the packets in transmitted order. The
driver can insert empty packets with <em class="structfield"><code>id</code></em> set
to zero anywhere in the packet array.</p><p>To assure synchronization and to distinguish from frame
dropping, when a captured frame does not carry any of the requested
data services drivers must pass one or more empty packets. When an
application fails to pass VBI data in time for output, the driver
must output the last VPS and WSS packet again, and disable the output
of Closed Caption and Teletext data, or output data which is ignored
by Closed Caption and Teletext decoders.</p><p>A sliced VBI device may support <a class="link" href="ch03.html#rw" title="Read/Write">read/write</a> and/or streaming (<a class="link" href="ch03s02.html" title="Streaming I/O (Memory Mapping)">memory mapping</a> and/or <a class="link" href="ch03s03.html" title="Streaming I/O (User Pointers)">user
pointer</a>) I/O. The latter bears the possibility of synchronizing
video and VBI data by using buffer timestamps.</p></div><div class="section" title="Sliced VBI Data in MPEG Streams"><div class="titlepage"><div><div><h3 class="title"><a id="id2660280"></a>Sliced VBI Data in MPEG Streams</h3></div></div></div><div class="toc"><dl><dt><span class="section"><a href="ch04s08.html#id2660362">MPEG Stream Embedded, Sliced VBI Data Format: NONE</a></span></dt><dt><span class="section"><a href="ch04s08.html#id2660387">MPEG Stream Embedded, Sliced VBI Data Format: IVTV</a></span></dt></dl></div><p>If a device can produce an MPEG output stream, it may be
capable of providing <a class="link" href="ch04s08.html#sliced-vbi-format-negotitation" title="Sliced VBI Format Negotiation">negotiated sliced VBI
services</a> as data embedded in the MPEG stream. Users or
applications control this sliced VBI data insertion with the <a class="link" href="ch01s09.html#v4l2-mpeg-stream-vbi-fmt">V4L2_CID_MPEG_STREAM_VBI_FMT</a>
control.</p><p>If the driver does not provide the <a class="link" href="ch01s09.html#v4l2-mpeg-stream-vbi-fmt">V4L2_CID_MPEG_STREAM_VBI_FMT</a>
control, or only allows that control to be set to <a class="link" href="ch01s09.html#v4l2-mpeg-stream-vbi-fmt"><code class="constant">
V4L2_MPEG_STREAM_VBI_FMT_NONE</code></a>, then the device
cannot embed sliced VBI data in the MPEG stream.</p><p>The <a class="link" href="ch01s09.html#v4l2-mpeg-stream-vbi-fmt">
V4L2_CID_MPEG_STREAM_VBI_FMT</a> control does not implicitly set
the device driver to capture nor cease capturing sliced VBI data. The
control only indicates to embed sliced VBI data in the MPEG stream, if
an application has negotiated sliced VBI service be captured.</p><p>It may also be the case that a device can embed sliced VBI
data in only certain types of MPEG streams: for example in an MPEG-2
PS but not an MPEG-2 TS. In this situation, if sliced VBI data
insertion is requested, the sliced VBI data will be embedded in MPEG
stream types when supported, and silently omitted from MPEG stream
types where sliced VBI data insertion is not supported by the device.
</p><p>The following subsections specify the format of the
embedded sliced VBI data.</p><div class="section" title="MPEG Stream Embedded, Sliced VBI Data Format: NONE"><div class="titlepage"><div><div><h4 class="title"><a id="id2660362"></a>MPEG Stream Embedded, Sliced VBI Data Format: NONE</h4></div></div></div><p>The <a class="link" href="ch01s09.html#v4l2-mpeg-stream-vbi-fmt"><code class="constant">
V4L2_MPEG_STREAM_VBI_FMT_NONE</code></a> embedded sliced VBI
format shall be interpreted by drivers as a control to cease
embedding sliced VBI data in MPEG streams. Neither the device nor
driver shall insert "empty" embedded sliced VBI data packets in the
MPEG stream when this format is set. No MPEG stream data structures
are specified for this format.</p></div><div class="section" title="MPEG Stream Embedded, Sliced VBI Data Format: IVTV"><div class="titlepage"><div><div><h4 class="title"><a id="id2660387"></a>MPEG Stream Embedded, Sliced VBI Data Format: IVTV</h4></div></div></div><p>The <a class="link" href="ch01s09.html#v4l2-mpeg-stream-vbi-fmt"><code class="constant">
V4L2_MPEG_STREAM_VBI_FMT_IVTV</code></a> embedded sliced VBI
format, when supported, indicates to the driver to embed up to 36
lines of sliced VBI data per frame in an MPEG-2 <span class="emphasis"><em>Private
Stream 1 PES</em></span> packet encapsulated in an MPEG-2 <span class="emphasis"><em>
Program Pack</em></span> in the MPEG stream.</p><p><span class="emphasis"><em>Historical context</em></span>: This format
specification originates from a custom, embedded, sliced VBI data
format used by the <code class="filename">ivtv</code> driver. This format
has already been informally specified in the kernel sources in the
file <code class="filename">Documentation/video4linux/cx2341x/README.vbi</code>
. The maximum size of the payload and other aspects of this format
are driven by the CX23415 MPEG decoder's capabilities and limitations
with respect to extracting, decoding, and displaying sliced VBI data
embedded within an MPEG stream.</p><p>This format's use is <span class="emphasis"><em>not</em></span> exclusive to
the <code class="filename">ivtv</code> driver <span class="emphasis"><em>nor</em></span>
exclusive to CX2341x devices, as the sliced VBI data packet insertion
into the MPEG stream is implemented in driver software. At least the
<code class="filename">cx18</code> driver provides sliced VBI data insertion
into an MPEG-2 PS in this format as well.</p><p>The following definitions specify the payload of the
MPEG-2 <span class="emphasis"><em>Private Stream 1 PES</em></span> packets that contain
sliced VBI data when <a class="link" href="ch01s09.html#v4l2-mpeg-stream-vbi-fmt">
<code class="constant">V4L2_MPEG_STREAM_VBI_FMT_IVTV</code></a> is set.
(The MPEG-2 <span class="emphasis"><em>Private Stream 1 PES</em></span> packet header
and encapsulating MPEG-2 <span class="emphasis"><em>Program Pack</em></span> header are
not detailed here. Please refer to the MPEG-2 specifications for
details on those packet headers.)</p><p>The payload of the MPEG-2 <span class="emphasis"><em>Private Stream 1 PES
</em></span> packets that contain sliced VBI data is specified by
struct <a class="link" href="ch04s08.html#v4l2-mpeg-vbi-fmt-ivtv" title="Table 4.9. struct v4l2_mpeg_vbi_fmt_ivtv">v4l2_mpeg_vbi_fmt_ivtv</a>. The payload is variable
length, depending on the actual number of lines of sliced VBI data
present in a video frame. The payload may be padded at the end with
unspecified fill bytes to align the end of the payload to a 4-byte
boundary. The payload shall never exceed 1552 bytes (2 fields with
18 lines/field with 43 bytes of data/line and a 4 byte magic number).
</p><div class="table"><a id="v4l2-mpeg-vbi-fmt-ivtv"></a><p class="title"><b>Table 4.9. struct <span class="structname">v4l2_mpeg_vbi_fmt_ivtv</span>
</b></p><div class="table-contents"><table summary="struct v4l2_mpeg_vbi_fmt_ivtv " width="100%" border="0"><colgroup><col /><col /><col /><col /></colgroup><tbody valign="top"><tr><td valign="top">__u8</td><td valign="top"><em class="structfield"><code>magic</code></em>[4]</td><td valign="top"> </td><td valign="top">A "magic" constant from <a class="xref" href="ch04s08.html#v4l2-mpeg-vbi-fmt-ivtv-magic" title="Table 4.10. Magic Constants for struct v4l2_mpeg_vbi_fmt_ivtv magic field">Table 4.10, “Magic Constants for struct v4l2_mpeg_vbi_fmt_ivtv
<em class="structfield"><code>magic</code></em> field”</a> that indicates
this is a valid sliced VBI data payload and also indicates which
member of the anonymous union, <em class="structfield"><code>itv0</code></em> or
<em class="structfield"><code>ITV0</code></em>, to use for the payload data.</td></tr><tr><td valign="top">union</td><td valign="top">(anonymous)</td><td class="auto-generated"> </td><td class="auto-generated"> </td></tr><tr><td valign="top"> </td><td valign="top">struct <a class="link" href="ch04s08.html#v4l2-mpeg-vbi-itv0" title="Table 4.11. struct v4l2_mpeg_vbi_itv0">
<span class="structname">v4l2_mpeg_vbi_itv0</span></a>
</td><td valign="top"><em class="structfield"><code>itv0</code></em></td><td valign="top">The primary form of the sliced VBI data payload
that contains anywhere from 1 to 35 lines of sliced VBI data.
Line masks are provided in this form of the payload indicating
which VBI lines are provided.</td></tr><tr><td valign="top"> </td><td valign="top">struct <a class="link" href="ch04s08.html#v4l2-mpeg-vbi-itv0-1" title="Table 4.12. struct v4l2_mpeg_vbi_ITV0">
<span class="structname">v4l2_mpeg_vbi_ITV0</span></a>
</td><td valign="top"><em class="structfield"><code>ITV0</code></em></td><td valign="top">An alternate form of the sliced VBI data payload
used when 36 lines of sliced VBI data are present. No line masks are
provided in this form of the payload; all valid line mask bits are
implcitly set.</td></tr></tbody></table></div></div><br class="table-break" /><div class="table"><a id="v4l2-mpeg-vbi-fmt-ivtv-magic"></a><p class="title"><b>Table 4.10. Magic Constants for struct <a class="link" href="ch04s08.html#v4l2-mpeg-vbi-fmt-ivtv" title="Table 4.9. struct v4l2_mpeg_vbi_fmt_ivtv">v4l2_mpeg_vbi_fmt_ivtv</a>
<em class="structfield"><code>magic</code></em> field</b></p><div class="table-contents"><table summary="Magic Constants for struct v4l2_mpeg_vbi_fmt_ivtv 	magic field" width="100%" border="0"><colgroup><col /><col /><col /></colgroup><thead><tr><th align="left">Defined Symbol</th><th align="left">Value</th><th align="left">Description</th></tr></thead><tbody valign="top"><tr><td valign="top"><code class="constant">V4L2_MPEG_VBI_IVTV_MAGIC0</code>
</td><td valign="top">"itv0"</td><td valign="top">Indicates the <em class="structfield"><code>itv0</code></em>
member of the union in struct <a class="link" href="ch04s08.html#v4l2-mpeg-vbi-fmt-ivtv" title="Table 4.9. struct v4l2_mpeg_vbi_fmt_ivtv">v4l2_mpeg_vbi_fmt_ivtv</a> is valid.</td></tr><tr><td valign="top"><code class="constant">V4L2_MPEG_VBI_IVTV_MAGIC1</code>
</td><td valign="top">"ITV0"</td><td valign="top">Indicates the <em class="structfield"><code>ITV0</code></em>
member of the union in struct <a class="link" href="ch04s08.html#v4l2-mpeg-vbi-fmt-ivtv" title="Table 4.9. struct v4l2_mpeg_vbi_fmt_ivtv">v4l2_mpeg_vbi_fmt_ivtv</a> is valid and
that 36 lines of sliced VBI data are present.</td></tr></tbody></table></div></div><br class="table-break" /><div class="table"><a id="v4l2-mpeg-vbi-itv0"></a><p class="title"><b>Table 4.11. struct <span class="structname">v4l2_mpeg_vbi_itv0</span>
</b></p><div class="table-contents"><table summary="struct v4l2_mpeg_vbi_itv0 " width="100%" border="0"><colgroup><col /><col /><col /></colgroup><tbody valign="top"><tr><td valign="top">__le32</td><td valign="top"><em class="structfield"><code>linemask</code></em>[2]</td><td valign="top"><p>Bitmasks indicating the VBI service lines
present. These <em class="structfield"><code>linemask</code></em> values are stored
in little endian byte order in the MPEG stream. Some reference
<em class="structfield"><code>linemask</code></em> bit positions with their
corresponding VBI line number and video field are given below.
b<sub>0</sub> indicates the least significant bit of a
<em class="structfield"><code>linemask</code></em> value:</p><pre class="screen">
<em class="structfield"><code>linemask</code></em>[0] b<sub>0</sub>: line 6 first field
<em class="structfield"><code>linemask</code></em>[0] b<sub>17</sub>: line 23 first field
<em class="structfield"><code>linemask</code></em>[0] b<sub>18</sub>: line 6 second field
<em class="structfield"><code>linemask</code></em>[0] b<sub>31</sub>: line 19 second field
<em class="structfield"><code>linemask</code></em>[1] b<sub>0</sub>: line 20 second field
<em class="structfield"><code>linemask</code></em>[1] b<sub>3</sub>: line 23 second field
<em class="structfield"><code>linemask</code></em>[1] b<sub>4</sub>-b<sub>31</sub>: unused and set to 0</pre></td></tr><tr><td valign="top">struct <a class="link" href="ch04s08.html#v4l2-mpeg-vbi-itv0-line" title="Table 4.13. struct v4l2_mpeg_vbi_itv0_line">
<span class="structname">v4l2_mpeg_vbi_itv0_line</span></a>
</td><td valign="top"><em class="structfield"><code>line</code></em>[35]</td><td valign="top">This is a variable length array that holds from 1
to 35 lines of sliced VBI data. The sliced VBI data lines present
correspond to the bits set in the <em class="structfield"><code>linemask</code></em>
array, starting from b<sub>0</sub> of <em class="structfield"><code>
linemask</code></em>[0] up through b<sub>31</sub> of
<em class="structfield"><code>linemask</code></em>[0], and from b<sub>0
</sub> of <em class="structfield"><code>linemask</code></em>[1] up through b
<sub>3</sub> of <em class="structfield"><code>linemask</code></em>[1].
<em class="structfield"><code>line</code></em>[0] corresponds to the first bit
found set in the <em class="structfield"><code>linemask</code></em> array,
<em class="structfield"><code>line</code></em>[1] corresponds to the second bit
found set in the <em class="structfield"><code>linemask</code></em> array, etc.
If no <em class="structfield"><code>linemask</code></em> array bits are set, then
<em class="structfield"><code>line</code></em>[0] may contain one line of
unspecified data that should be ignored by applications.</td></tr></tbody></table></div></div><br class="table-break" /><div class="table"><a id="v4l2-mpeg-vbi-itv0-1"></a><p class="title"><b>Table 4.12. struct <span class="structname">v4l2_mpeg_vbi_ITV0</span>
</b></p><div class="table-contents"><table summary="struct v4l2_mpeg_vbi_ITV0 " width="100%" border="0"><colgroup><col /><col /><col /></colgroup><tbody valign="top"><tr><td valign="top">struct <a class="link" href="ch04s08.html#v4l2-mpeg-vbi-itv0-line" title="Table 4.13. struct v4l2_mpeg_vbi_itv0_line">
<span class="structname">v4l2_mpeg_vbi_itv0_line</span></a>
</td><td valign="top"><em class="structfield"><code>line</code></em>[36]</td><td valign="top">A fixed length array of 36 lines of sliced VBI
data. <em class="structfield"><code>line</code></em>[0] through <em class="structfield"><code>line
</code></em>[17] correspond to lines 6 through 23 of the
first field. <em class="structfield"><code>line</code></em>[18] through
<em class="structfield"><code>line</code></em>[35] corresponds to lines 6
through 23 of the second field.</td></tr></tbody></table></div></div><br class="table-break" /><div class="table"><a id="v4l2-mpeg-vbi-itv0-line"></a><p class="title"><b>Table 4.13. struct <span class="structname">v4l2_mpeg_vbi_itv0_line</span>
</b></p><div class="table-contents"><table summary="struct v4l2_mpeg_vbi_itv0_line " width="100%" border="0"><colgroup><col /><col /><col /></colgroup><tbody valign="top"><tr><td valign="top">__u8</td><td valign="top"><em class="structfield"><code>id</code></em></td><td valign="top">A line identifier value from
<a class="xref" href="ch04s08.html#ITV0-Line-Identifier-Constants" title="Table 4.14. Line Identifiers for struct v4l2_mpeg_vbi_itv0_line id field">Table 4.14, “Line Identifiers for struct <span class="structname">
v4l2_mpeg_vbi_itv0_line</span> <em class="structfield"><code>id
</code></em> field”</a> that indicates
the type of sliced VBI data stored on this line.</td></tr><tr><td valign="top">__u8</td><td valign="top"><em class="structfield"><code>data</code></em>[42]</td><td valign="top">The sliced VBI data for the line.</td></tr></tbody></table></div></div><br class="table-break" /><div class="table"><a id="ITV0-Line-Identifier-Constants"></a><p class="title"><b>Table 4.14. Line Identifiers for struct <a class="link" href="ch04s08.html#v4l2-mpeg-vbi-itv0-line" title="Table 4.13. struct v4l2_mpeg_vbi_itv0_line"><span class="structname">
v4l2_mpeg_vbi_itv0_line</span></a> <em class="structfield"><code>id
</code></em> field</b></p><div class="table-contents"><table summary="Line Identifiers for struct v4l2_mpeg_vbi_itv0_line id field" width="100%" border="0"><colgroup><col /><col /><col /></colgroup><thead><tr><th align="left">Defined Symbol</th><th align="left">Value</th><th align="left">Description</th></tr></thead><tbody valign="top"><tr><td valign="top"><code class="constant">V4L2_MPEG_VBI_IVTV_TELETEXT_B</code>
</td><td valign="top">1</td><td valign="top">Refer to <a class="link" href="ch04s08.html#vbi-services2" title="Table 4.7. Sliced VBI services">
Sliced VBI services</a> for a description of the line payload.</td></tr><tr><td valign="top"><code class="constant">V4L2_MPEG_VBI_IVTV_CAPTION_525</code>
</td><td valign="top">4</td><td valign="top">Refer to <a class="link" href="ch04s08.html#vbi-services2" title="Table 4.7. Sliced VBI services">
Sliced VBI services</a> for a description of the line payload.</td></tr><tr><td valign="top"><code class="constant">V4L2_MPEG_VBI_IVTV_WSS_625</code>
</td><td valign="top">5</td><td valign="top">Refer to <a class="link" href="ch04s08.html#vbi-services2" title="Table 4.7. Sliced VBI services">
Sliced VBI services</a> for a description of the line payload.</td></tr><tr><td valign="top"><code class="constant">V4L2_MPEG_VBI_IVTV_VPS</code>
</td><td valign="top">7</td><td valign="top">Refer to <a class="link" href="ch04s08.html#vbi-services2" title="Table 4.7. Sliced VBI services">
Sliced VBI services</a> for a description of the line payload.</td></tr></tbody></table></div></div><br class="table-break" /></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch04s07.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch04.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch04s09.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Raw VBI Data Interface </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Teletext Interface</td></tr></table></div></body></html>
